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 $55.98   9.448%   $61.269   $61.27   $61.25   $61.30  
  Purchase #2 $148.92   4.655%   $155.8522   $155.85   $155.85   $155.90  
  Purchase #3 $144.84   7.218%   $155.2946   $155.29   $155.30   $155.30  
  Purchase #4 $70.29   5.759%   $74.338   $74.34   $74.35   $74.30  
  Purchase #5 $29.65   13.547%   $33.6667   $33.67   $33.65   $33.70  
  Purchase #6 $217.44   6.118%   $230.743   $230.74   $230.75   $230.70  
  Purchase #7 $54.40   8.789%   $59.1812   $59.18   $59.20   $59.20  
  7 purchase totals = $721.52       $770.3447   $770.34   $770.35   $770.40