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 $231.42   8.534%   $251.1694   $251.17   $251.15   $251.20  
  Purchase #2 $173.31   8.836%   $188.6237   $188.62   $188.60   $188.60  
  Purchase #3 $210.53   7.248%   $225.7892   $225.79   $225.80   $225.80  
  Purchase #4 $57.52   6.488%   $61.2519   $61.25   $61.25   $61.30  
  Purchase #5 $183.52   9.707%   $201.3343   $201.33   $201.35   $201.30  
  Purchase #6 $171.32   5.143%   $180.131   $180.13   $180.15   $180.10  
  Purchase #7 $54.32   13.303%   $61.5462   $61.55   $61.55   $61.50  
  7 purchase totals = $1,081.94       $1,169.8457   $1,169.84   $1,169.85   $1,169.80