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 $50.32   4.732%   $52.7011   $52.70   $52.70   $52.70  
  Purchase #2 $182.56   11.193%   $202.9939   $202.99   $203.00   $203.00  
  Purchase #3 $246.60   10.444%   $272.3549   $272.35   $272.35   $272.40  
  Purchase #4 $88.28   9.257%   $96.4521   $96.45   $96.45   $96.50  
  Purchase #5 $154.55   7.848%   $166.6791   $166.68   $166.70   $166.70  
  Purchase #6 $41.94   9.772%   $46.0384   $46.04   $46.05   $46.00  
  Purchase #7 $143.82   10.534%   $158.97   $158.97   $158.95   $159.00  
  7 purchase totals = $908.07       $996.1895   $996.18   $996.20   $996.30