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 $158.70   4.810%   $166.3335   $166.33   $166.35   $166.30  
  Purchase #2 $233.59   3.437%   $241.6185   $241.62   $241.60   $241.60  
  Purchase #3 $47.39   4.638%   $49.5879   $49.59   $49.60   $49.60  
  Purchase #4 $151.29   12.193%   $169.7368   $169.74   $169.75   $169.70  
  Purchase #5 $197.52   9.605%   $216.4918   $216.49   $216.50   $216.50  
  Purchase #6 $110.25   10.695%   $122.0412   $122.04   $122.05   $122.00  
  Purchase #7 $58.93   13.331%   $66.786   $66.79   $66.80   $66.80  
  7 purchase totals = $957.67       $1,032.5957   $1,032.60   $1,032.65   $1,032.50