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 $160.93   10.210%   $177.361   $177.36   $177.35   $177.40  
  Purchase #2 $123.94   7.442%   $133.1636   $133.16   $133.15   $133.20  
  Purchase #3 $52.84   8.304%   $57.2278   $57.23   $57.25   $57.20  
  Purchase #4 $181.84   10.302%   $200.5732   $200.57   $200.55   $200.60  
  Purchase #5 $236.71   12.419%   $266.107   $266.11   $266.10   $266.10  
  Purchase #6 $217.78   6.635%   $232.2297   $232.23   $232.25   $232.20  
  Purchase #7 $23.98   9.837%   $26.3389   $26.34   $26.35   $26.30  
  7 purchase totals = $998.02       $1,093.0012   $1,093.00   $1,093.00   $1,093.00