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 $56.57   4.380%   $59.0478   $59.05   $59.05   $59.00  
  Purchase #2 $98.42   4.179%   $102.533   $102.53   $102.55   $102.50  
  Purchase #3 $99.34   7.226%   $106.5183   $106.52   $106.50   $106.50  
  Purchase #4 $172.31   4.541%   $180.1346   $180.13   $180.15   $180.10  
  Purchase #5 $200.94   8.831%   $218.685   $218.69   $218.70   $218.70  
  Purchase #6 $54.88   3.557%   $56.8321   $56.83   $56.85   $56.80  
  Purchase #7 $52.35   11.201%   $58.2137   $58.21   $58.20   $58.20  
  7 purchase totals = $734.81       $781.9645   $781.96   $782.00   $781.80