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 $220.96   11.650%   $246.7018   $246.70   $246.70   $246.70  
  Purchase #2 $38.92   7.229%   $41.7335   $41.73   $41.75   $41.70  
  Purchase #3 $69.53   3.742%   $72.1318   $72.13   $72.15   $72.10  
  Purchase #4 $187.84   5.495%   $198.1618   $198.16   $198.15   $198.20  
  Purchase #5 $209.84   3.317%   $216.8004   $216.80   $216.80   $216.80  
  Purchase #6 $249.53   12.625%   $281.0332   $281.03   $281.05   $281.00  
  Purchase #7 $172.55   12.153%   $193.52   $193.52   $193.50   $193.50  
  7 purchase totals = $1,149.17       $1,250.0825   $1,250.07   $1,250.10   $1,250.00