Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $123.77   4.415%   $129.2344   $129.23   $129.25   $129.20  
  Purchase #2 $112.65   4.647%   $117.8848   $117.88   $117.90   $117.90  
  Purchase #3 $227.90   7.571%   $245.1543   $245.15   $245.15   $245.20  
  Purchase #4 $170.98   8.111%   $184.8482   $184.85   $184.85   $184.80  
  Purchase #5 $129.41   9.697%   $141.9589   $141.96   $141.95   $142.00  
  Purchase #6 $147.97   12.298%   $166.1674   $166.17   $166.15   $166.20  
  Purchase #7 $99.48   9.305%   $108.7366   $108.74   $108.75   $108.70  
  7 purchase totals = $1,012.16       $1,093.9846   $1,093.98   $1,094.00   $1,094.00