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 $76.74   10.783%   $85.0149   $85.01   $85.00   $85.00  
  Purchase #2 $195.74   3.766%   $203.1116   $203.11   $203.10   $203.10  
  Purchase #3 $56.58   8.326%   $61.2909   $61.29   $61.30   $61.30  
  Purchase #4 $212.87   6.170%   $226.0041   $226.00   $226.00   $226.00  
  Purchase #5 $186.92   9.358%   $204.412   $204.41   $204.40   $204.40  
  Purchase #6 $133.60   10.796%   $148.0235   $148.02   $148.00   $148.00  
  Purchase #7 $171.29   9.148%   $186.9596   $186.96   $186.95   $187.00  
  7 purchase totals = $1,033.74       $1,114.8166   $1,114.80   $1,114.75   $1,114.80