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 $225.96   9.244%   $246.8477   $246.85   $246.85   $246.80  
  Purchase #2 $10.54   7.826%   $11.3649   $11.36   $11.35   $11.40  
  Purchase #3 $170.34   4.256%   $177.5897   $177.59   $177.60   $177.60  
  Purchase #4 $185.29   13.606%   $210.5006   $210.50   $210.50   $210.50  
  Purchase #5 $120.33   3.541%   $124.5909   $124.59   $124.60   $124.60  
  Purchase #6 $202.98   11.379%   $226.0771   $226.08   $226.10   $226.10  
  Purchase #7 $233.33   7.826%   $251.5904   $251.59   $251.60   $251.60  
  7 purchase totals = $1,148.77       $1,248.5613   $1,248.56   $1,248.60   $1,248.60