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 $155.29   10.308%   $171.2973   $171.30   $171.30   $171.30  
  Purchase #2 $217.62   8.121%   $235.2929   $235.29   $235.30   $235.30  
  Purchase #3 $229.98   11.574%   $256.5979   $256.60   $256.60   $256.60  
  Purchase #4 $102.93   3.744%   $106.7837   $106.78   $106.80   $106.80  
  Purchase #5 $94.90   9.125%   $103.5596   $103.56   $103.55   $103.60  
  Purchase #6 $133.68   9.872%   $146.8769   $146.88   $146.90   $146.90  
  Purchase #7 $39.97   4.180%   $41.6407   $41.64   $41.65   $41.60  
  7 purchase totals = $974.37       $1,062.0490   $1,062.05   $1,062.10   $1,062.10