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 $196.79   5.521%   $207.6548   $207.65   $207.65   $207.70  
  Purchase #2 $30.64   7.702%   $32.9999   $33.00   $33.00   $33.00  
  Purchase #3 $77.33   3.751%   $80.2306   $80.23   $80.25   $80.20  
  Purchase #4 $14.96   9.494%   $16.3803   $16.38   $16.40   $16.40  
  Purchase #5 $211.67   9.732%   $232.2697   $232.27   $232.25   $232.30  
  Purchase #6 $109.78   12.760%   $123.7879   $123.79   $123.80   $123.80  
  Purchase #7 $52.76   13.664%   $59.9691   $59.97   $59.95   $60.00  
  7 purchase totals = $693.93       $753.2923   $753.29   $753.30   $753.40