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 $107.53   11.135%   $119.5035   $119.50   $119.50   $119.50  
  Purchase #2 $186.58   4.415%   $194.8175   $194.82   $194.80   $194.80  
  Purchase #3 $145.35   8.502%   $157.7077   $157.71   $157.70   $157.70  
  Purchase #4 $60.88   6.707%   $64.9632   $64.96   $64.95   $65.00  
  Purchase #5 $179.70   6.580%   $191.5243   $191.52   $191.50   $191.50  
  Purchase #6 $187.30   13.309%   $212.2278   $212.23   $212.25   $212.20  
  Purchase #7 $109.59   5.356%   $115.4596   $115.46   $115.45   $115.50  
  7 purchase totals = $976.93       $1,056.2036   $1,056.20   $1,056.15   $1,056.20