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 $89.84   9.824%   $98.6659   $98.67   $98.65   $98.70  
  Purchase #2 $185.48   13.373%   $210.2842   $210.28   $210.30   $210.30  
  Purchase #3 $68.67   7.415%   $73.7619   $73.76   $73.75   $73.80  
  Purchase #4 $121.93   11.108%   $135.474   $135.47   $135.45   $135.50  
  Purchase #5 $36.76   12.639%   $41.4061   $41.41   $41.40   $41.40  
  Purchase #6 $212.45   4.486%   $221.9805   $221.98   $222.00   $222.00  
  Purchase #7 $211.64   6.158%   $224.6728   $224.67   $224.65   $224.70  
  7 purchase totals = $926.77       $1,006.2454   $1,006.24   $1,006.20   $1,006.40