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 $149.62   13.589%   $169.9519   $169.95   $169.95   $170.00  
  Purchase #2 $192.62   9.303%   $210.5394   $210.54   $210.55   $210.50  
  Purchase #3 $222.49   11.485%   $248.043   $248.04   $248.05   $248.00  
  Purchase #4 $81.59   8.661%   $88.6565   $88.66   $88.65   $88.70  
  Purchase #5 $108.49   12.779%   $122.3539   $122.35   $122.35   $122.40  
  Purchase #6 $85.52   8.309%   $92.6259   $92.63   $92.65   $92.60  
  Purchase #7 $70.71   5.718%   $74.7532   $74.75   $74.75   $74.80  
  7 purchase totals = $911.04       $1,006.9238   $1,006.92   $1,006.95   $1,007.00