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 $62.98   9.725%   $69.1048   $69.10   $69.10   $69.10  
  Purchase #2 $27.78   6.187%   $29.4987   $29.50   $29.50   $29.50  
  Purchase #3 $71.68   12.610%   $80.7188   $80.72   $80.70   $80.70  
  Purchase #4 $167.68   5.776%   $177.3652   $177.37   $177.35   $177.40  
  Purchase #5 $117.39   3.413%   $121.3965   $121.40   $121.40   $121.40  
  Purchase #6 $205.43   11.174%   $228.3847   $228.38   $228.40   $228.40  
  Purchase #7 $54.79   9.235%   $59.8499   $59.85   $59.85   $59.80  
  7 purchase totals = $707.73       $766.3186   $766.32   $766.30   $766.30