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 $33.65   12.161%   $37.7422   $37.74   $37.75   $37.70  
  Purchase #2 $194.60   9.177%   $212.4584   $212.46   $212.45   $212.50  
  Purchase #3 $213.28   6.664%   $227.493   $227.49   $227.50   $227.50  
  Purchase #4 $86.65   7.550%   $93.1921   $93.19   $93.20   $93.20  
  Purchase #5 $250.37   7.779%   $269.8463   $269.85   $269.85   $269.80  
  Purchase #6 $183.52   11.137%   $203.9586   $203.96   $203.95   $204.00  
  Purchase #7 $206.37   12.112%   $231.3655   $231.37   $231.35   $231.40  
  7 purchase totals = $1,168.44       $1,276.0561   $1,276.06   $1,276.05   $1,276.10