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 $189.52   8.581%   $205.7827   $205.78   $205.80   $205.80  
  Purchase #2 $194.26   8.287%   $210.3583   $210.36   $210.35   $210.40  
  Purchase #3 $226.73   7.240%   $243.1453   $243.15   $243.15   $243.10  
  Purchase #4 $175.32   12.686%   $197.5611   $197.56   $197.55   $197.60  
  Purchase #5 $88.98   3.307%   $91.9226   $91.92   $91.90   $91.90  
  Purchase #6 $201.60   9.234%   $220.2157   $220.22   $220.20   $220.20  
  Purchase #7 $184.88   3.311%   $191.0014   $191.00   $191.00   $191.00  
  7 purchase totals = $1,261.29       $1,359.9871   $1,359.99   $1,359.95   $1,360.00