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 $182.31   11.809%   $203.839   $203.84   $203.85   $203.80  
  Purchase #2 $136.84   9.410%   $149.7166   $149.72   $149.70   $149.70  
  Purchase #3 $102.57   7.187%   $109.9417   $109.94   $109.95   $109.90  
  Purchase #4 $54.96   11.294%   $61.1672   $61.17   $61.15   $61.20  
  Purchase #5 $126.27   7.180%   $135.3362   $135.34   $135.35   $135.30  
  Purchase #6 $44.39   12.296%   $49.8482   $49.85   $49.85   $49.80  
  Purchase #7 $186.88   9.690%   $204.9887   $204.99   $205.00   $205.00  
  7 purchase totals = $834.22       $914.8376   $914.85   $914.85   $914.70