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 $191.86   5.112%   $201.6679   $201.67   $201.65   $201.70  
  Purchase #2 $86.62   4.801%   $90.7786   $90.78   $90.80   $90.80  
  Purchase #3 $92.95   9.511%   $101.7905   $101.79   $101.80   $101.80  
  Purchase #4 $118.91   11.650%   $132.763   $132.76   $132.75   $132.80  
  Purchase #5 $153.49   6.857%   $164.0148   $164.01   $164.00   $164.00  
  Purchase #6 $190.71   11.485%   $212.613   $212.61   $212.60   $212.60  
  Purchase #7 $171.30   4.841%   $179.5926   $179.59   $179.60   $179.60  
  7 purchase totals = $1,005.84       $1,083.2204   $1,083.21   $1,083.20   $1,083.30