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 $34.29   9.814%   $37.6552   $37.66   $37.65   $37.70  
  Purchase #2 $235.33   6.709%   $251.1183   $251.12   $251.10   $251.10  
  Purchase #3 $212.98   3.623%   $220.6963   $220.70   $220.70   $220.70  
  Purchase #4 $225.50   9.791%   $247.5787   $247.58   $247.60   $247.60  
  Purchase #5 $23.82   13.655%   $27.0726   $27.07   $27.05   $27.10  
  Purchase #6 $151.66   6.673%   $161.7803   $161.78   $161.80   $161.80  
  Purchase #7 $187.83   9.854%   $206.3388   $206.34   $206.35   $206.30  
  7 purchase totals = $1,071.41       $1,152.2402   $1,152.25   $1,152.25   $1,152.30