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 $176.57   11.578%   $197.0133   $197.01   $197.00   $197.00  
  Purchase #2 $41.67   4.225%   $43.4306   $43.43   $43.45   $43.40  
  Purchase #3 $243.65   7.842%   $262.757   $262.76   $262.75   $262.80  
  Purchase #4 $24.67   9.629%   $27.0455   $27.05   $27.05   $27.00  
  Purchase #5 $139.52   9.717%   $153.0772   $153.08   $153.10   $153.10  
  Purchase #6 $84.72   5.780%   $89.6168   $89.62   $89.60   $89.60  
  Purchase #7 $250.90   11.467%   $279.6707   $279.67   $279.65   $279.70  
  7 purchase totals = $961.70       $1,052.6111   $1,052.62   $1,052.60   $1,052.60