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 $127.53   5.604%   $134.6768   $134.68   $134.70   $134.70  
  Purchase #2 $228.60   11.631%   $255.1885   $255.19   $255.20   $255.20  
  Purchase #3 $225.96   9.696%   $247.8691   $247.87   $247.85   $247.90  
  Purchase #4 $182.41   13.415%   $206.8803   $206.88   $206.90   $206.90  
  Purchase #5 $70.28   5.305%   $74.0084   $74.01   $74.00   $74.00  
  Purchase #6 $151.96   9.700%   $166.7001   $166.70   $166.70   $166.70  
  Purchase #7 $85.92   6.803%   $91.7651   $91.77   $91.75   $91.80  
  7 purchase totals = $1,072.66       $1,177.0883   $1,177.10   $1,177.10   $1,177.20