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 $69.74   8.566%   $75.7139   $75.71   $75.70   $75.70  
  Purchase #2 $230.96   12.222%   $259.1879   $259.19   $259.20   $259.20  
  Purchase #3 $234.70   7.309%   $251.8542   $251.85   $251.85   $251.90  
  Purchase #4 $32.93   3.795%   $34.1797   $34.18   $34.20   $34.20  
  Purchase #5 $53.58   12.244%   $60.1403   $60.14   $60.15   $60.10  
  Purchase #6 $33.53   10.718%   $37.1237   $37.12   $37.10   $37.10  
  Purchase #7 $115.85   9.638%   $127.0156   $127.02   $127.00   $127.00  
  7 purchase totals = $771.29       $845.2153   $845.21   $845.20   $845.20