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 $5.88   3.375%   $6.0785   $6.08   $6.10   $6.10  
  Purchase #2 $174.41   12.205%   $195.6967   $195.70   $195.70   $195.70  
  Purchase #3 $192.69   4.329%   $201.0316   $201.03   $201.05   $201.00  
  Purchase #4 $184.45   5.794%   $195.137   $195.14   $195.15   $195.10  
  Purchase #5 $83.84   12.341%   $94.1867   $94.19   $94.20   $94.20  
  Purchase #6 $165.95   13.600%   $188.5192   $188.52   $188.50   $188.50  
  Purchase #7 $191.51   10.781%   $212.1567   $212.16   $212.15   $212.20  
  7 purchase totals = $998.73       $1,092.8064   $1,092.82   $1,092.85   $1,092.80