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 $158.42   7.198%   $169.8231   $169.82   $169.80   $169.80  
  Purchase #2 $99.44   10.284%   $109.6664   $109.67   $109.65   $109.70  
  Purchase #3 $152.55   11.471%   $170.049   $170.05   $170.05   $170.00  
  Purchase #4 $83.85   6.557%   $89.348   $89.35   $89.35   $89.30  
  Purchase #5 $136.59   8.648%   $148.4023   $148.40   $148.40   $148.40  
  Purchase #6 $166.40   12.465%   $187.1418   $187.14   $187.15   $187.10  
  Purchase #7 $203.52   7.481%   $218.7453   $218.75   $218.75   $218.70  
  7 purchase totals = $1,000.77       $1,093.1759   $1,093.18   $1,093.15   $1,093.00