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 $207.85   7.298%   $223.0189   $223.02   $223.00   $223.00  
  Purchase #2 $164.55   3.111%   $169.6692   $169.67   $169.65   $169.70  
  Purchase #3 $201.27   5.499%   $212.3378   $212.34   $212.35   $212.30  
  Purchase #4 $88.82   6.235%   $94.3579   $94.36   $94.35   $94.40  
  Purchase #5 $98.90   9.224%   $108.0225   $108.02   $108.00   $108.00  
  Purchase #6 $135.72   5.398%   $143.0462   $143.05   $143.05   $143.00  
  Purchase #7 $203.66   10.603%   $225.2541   $225.25   $225.25   $225.30  
  7 purchase totals = $1,100.77       $1,175.7066   $1,175.71   $1,175.65   $1,175.70