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 $118.44   3.115%   $122.1294   $122.13   $122.15   $122.10  
  Purchase #2 $26.44   12.221%   $29.6712   $29.67   $29.65   $29.70  
  Purchase #3 $106.35   11.244%   $118.308   $118.31   $118.30   $118.30  
  Purchase #4 $240.98   7.372%   $258.745   $258.75   $258.75   $258.70  
  Purchase #5 $142.26   4.352%   $148.4512   $148.45   $148.45   $148.50  
  Purchase #6 $222.43   6.461%   $236.8012   $236.80   $236.80   $236.80  
  Purchase #7 $93.43   4.666%   $97.7894   $97.79   $97.80   $97.80  
  7 purchase totals = $950.33       $1,011.8954   $1,011.90   $1,011.90   $1,011.90