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 $243.30   8.810%   $264.7347   $264.73   $264.75   $264.70  
  Purchase #2 $91.61   4.115%   $95.3798   $95.38   $95.40   $95.40  
  Purchase #3 $152.82   11.644%   $170.6144   $170.61   $170.60   $170.60  
  Purchase #4 $93.33   3.310%   $96.4192   $96.42   $96.40   $96.40  
  Purchase #5 $121.75   10.228%   $134.2026   $134.20   $134.20   $134.20  
  Purchase #6 $204.56   10.387%   $225.8076   $225.81   $225.80   $225.80  
  Purchase #7 $118.52   4.438%   $123.7799   $123.78   $123.80   $123.80  
  7 purchase totals = $1,025.89       $1,110.9382   $1,110.93   $1,110.95   $1,110.90