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 $189.45   11.759%   $211.7274   $211.73   $211.75   $211.70  
  Purchase #2 $245.95   10.854%   $272.6454   $272.65   $272.65   $272.60  
  Purchase #3 $28.31   11.205%   $31.4821   $31.48   $31.50   $31.50  
  Purchase #4 $196.78   8.570%   $213.644   $213.64   $213.65   $213.60  
  Purchase #5 $80.33   4.705%   $84.1095   $84.11   $84.10   $84.10  
  Purchase #6 $51.62   7.220%   $55.347   $55.35   $55.35   $55.30  
  Purchase #7 $141.81   10.601%   $156.8433   $156.84   $156.85   $156.80  
  7 purchase totals = $934.25       $1,025.7987   $1,025.80   $1,025.85   $1,025.60