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 $238.68   12.672%   $268.9255   $268.93   $268.95   $268.90  
  Purchase #2 $51.42   3.555%   $53.248   $53.25   $53.25   $53.20  
  Purchase #3 $193.58   6.320%   $205.8143   $205.81   $205.80   $205.80  
  Purchase #4 $218.53   12.678%   $246.2352   $246.24   $246.25   $246.20  
  Purchase #5 $24.56   5.796%   $25.9835   $25.98   $26.00   $26.00  
  Purchase #6 $170.95   12.666%   $192.6025   $192.60   $192.60   $192.60  
  Purchase #7 $87.89   4.107%   $91.4996   $91.50   $91.50   $91.50  
  7 purchase totals = $985.61       $1,084.3086   $1,084.31   $1,084.35   $1,084.20