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 $45.90   11.133%   $51.01   $51.01   $51.00   $51.00  
  Purchase #2 $153.77   10.121%   $169.3331   $169.33   $169.35   $169.30  
  Purchase #3 $58.49   10.545%   $64.6578   $64.66   $64.65   $64.70  
  Purchase #4 $210.82   3.547%   $218.2978   $218.30   $218.30   $218.30  
  Purchase #5 $129.52   11.718%   $144.6972   $144.70   $144.70   $144.70  
  Purchase #6 $149.28   10.222%   $164.5394   $164.54   $164.55   $164.50  
  Purchase #7 $165.99   13.288%   $188.0468   $188.05   $188.05   $188.00  
  7 purchase totals = $913.77       $1,000.5821   $1,000.59   $1,000.60   $1,000.50