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 $146.89   5.199%   $154.5268   $154.53   $154.55   $154.50  
  Purchase #2 $191.52   10.119%   $210.8999   $210.90   $210.90   $210.90  
  Purchase #3 $95.83   13.434%   $108.7038   $108.70   $108.70   $108.70  
  Purchase #4 $193.46   5.846%   $204.7697   $204.77   $204.75   $204.80  
  Purchase #5 $232.30   4.140%   $241.9172   $241.92   $241.90   $241.90  
  Purchase #6 $45.45   7.773%   $48.9828   $48.98   $49.00   $49.00  
  Purchase #7 $172.79   11.231%   $192.196   $192.20   $192.20   $192.20  
  7 purchase totals = $1,078.24       $1,161.9962   $1,162.00   $1,162.00   $1,162.00